The present invention disclosed herein relates to a laser device, and more particularly, to a multiple distributed feedback laser device.
Semiconductor-based optical devices may be manufactured using semiconductor processes such as a growth process, a photolithography process, and an etching process and/or a deposition process. By using the semiconductor processes, such a semiconductor-based optical device may be miniaturized and mass-produced. In addition, manufacturing costs thereof may be reduced. Accordingly, many researches with respect to the semiconductor-based optical device are being progressed.
Among the semiconductor-based optical devices, functional laser devices, which select specific wavelengths, such as a distributed feedback laser diode and/or a distributed bragg reflector laser diode are being developed. The functional laser devices may filter a wavelength using a diffraction grating. For example, only a lightwave having a specific wavelength corresponding to a bragg wavelength due to a periodic change of a refractive index may be reflected. Thus, the wavelength may be filtered. The reflected lightwave having the specific wavelength may be fed back into a gain region and oscillated. Such a functional laser device may be used as a light source for an optical communication system as well as a light source for generating a terahertz (THz) wave by photomixing.
In a method of generating the THz wave, there are various techniques such as a frequency doubling method, a backward wave oscillator, a photomixing method, carbon dioxide pumping gas laser, quantum cascade laser, and free electron laser. The photomixing method is a method in which beating signals of two laser diodes having wavelengths different from each other are incident onto a photomixer to secure a THz wave of a wavelength corresponding to a beating period thereof. To perform the photomixing method, a frequency of at least one of two laser beams must be stably sequentially tuned. Also, it may be required to accord characteristics of the two laser beams. To secure such a requirement, auxiliary devices are required. Thus, an apparatus of generating the THz wave using the photomixing method may become bigger, and a structure thereof may be complicated. Therefore, manufacturing costs may increase.